The present invention relates to a cathode ray tube for use as a television picture tube or the like.
An electron tube for projecting cathode rays to a face plate so as to produce an image on the face plate, i.e., a so-called cathode ray tube (hereinafter abbreviated as the CRT), is used for a television receiver, for example. The CRT has, in recent years, been most popularly used as a display unit for displaying video information.
FIG. 6 is a partial and side elevational view, partly in section, of an example of a conventional CRT. Illustrated in the drawing are a panel 1, which includes a face plate 1a disposed in the front and adapted to display an image thereon and a panel skirt 1b disposed in an outer periphery thereof in such a manner as to extend therefrom, and a funnel 2, which constitutes a side wall formed of glass and connected to a neck (not shown) incorporating an electron gun.
The panel 1 and the funnel 2 are joined at an adjoining surface 3 by means of glass soldering or the like. A metallic band 4 is wound around the panel skirt 1b.
In the production of a CRT thus constructed, it is necessary to reduce the internal pressure of the CRT and maintain its interior in a vacuum. At that juncture, a compressive stress and a tensile stress accompanying the pressure reduction occur in the panel 1 and the funnel 2.
FIG. 7, which is a partial perspective view of the CRT shown in FIG. 6, illustrates portions where a compressive stress and a tensile stress take place at the time of the reduction of internal pressure. A tensile stress ordinarily takes place in the shadowed portions in FIG. 7.
Generally, the glass constituting the panel 1 and the funnel 2 exhibit a high strength against the compressive stress, but exhibit a relatively low strength against the tensile stress. In particular, in a case where a fine flaw is present on an outer surface thereof, its strength against the tensile stress declines further. During the fabrication of the panel 1 and the funnel 2, damage leading to such a decline in tensile strength is liable to occur.
Thus, in the conventional CRT having the arrangement such as the one shown in FIG. 6, since the panel 1 and the funnel 2 are formed of glass, the strength against a tensile stress is low due to the reduction in the internal pressure. Therefore, in order to secure a sufficient strength, it is necessary to enlarge the thickness of the glass. This disadvantageously makes the CRT heavy in weight.
As another type of arrangement of a conventional CRT, as shown in FIG. 8, there is shown one which includes a glass panel 11 and a metallic funnel 12. Such a CRT is disclosed in, for instance, Japanese Patent Laid-Open No. 34983/1981. In such a CRT as well, tensile stress due to a pressure reduction takes place at a joint portion between the panel 11 and the funnel 12, presenting a problem similar to the one encountered with the CRT shown in FIG. 6.